Mapping Processes

Mapping a gene is not difficult so long as one understands some basic genetic terms and processes. To begin with, linked genes are genes located very near each other on the same chromosome. As crossing-over occurs, strongly linked genes rarely separate from each other whereas those loosely linked do. Using probability data from thousands of heredity experiment, geneticists can determine the likelihood of two linked genes splitting apart. This creates a series of sorts which can be mapped much like dates on a timeline. On a chromosome map, genes aren’t separated by distance, really, but by their linkage strength.

All 97 million-base genomes have been mapped in the Caenorhabditis elegans By permission NHGRI

Sequencing DNA is much more difficult. First, all 3 billion bases are divided into 100,000 groups, each with approximately 40,000 bases (some groups overlap). Then, each of the fragments is divided again into 100 pieces with 400 bases each. The precise order of the amino acids (adenine, guanine, cytosine, and thymine) is then determined for each 400 base sequence.